/**
 * The utillib library.
 * More information is available at http://www.jinchess.com/.
 * Copyright (C) 2003 Alexander Maryanovsky.
 * All rights reserved.
 *
 * The utillib library is free software; you can redistribute
 * it and/or modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * The utillib library is distributed in the hope that it will
 * be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
 * General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with utillib library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package free.util;

import java.util.Enumeration;
import java.util.NoSuchElementException;


/**
 * An implementation of the <code>Enumeration</code> interface which delegates
 * to another <code>Enumeration</code>, but only returns elements which pass
 * the {@link #accept(Object)} method.
 */

public abstract class FilteringEnumeration implements Enumeration {


    /**
     * The delegate enumeration.
     */

    private final Enumeration delegate;


    /**
     * The next element we'll return. This is set by the <code>findNext</code>
     * method.
     */

    private Object next = null;


    /**
     * Creates a new <code>FilteringEnumeration</code> object with the specified
     * delegate.
     */

    public FilteringEnumeration(Enumeration delegate) {
        this.delegate = delegate;
    }


    /**
     * Finds the next element in the delegate enumeration which passes
     * <code>accept</code> and puts it in <code>next</code>.
     */

    private void findNext() {
        if (next != null)
            return;

        while (delegate.hasMoreElements()) {
            Object element = delegate.nextElement();
            if (accept(element)) {
                next = element;
                break;
            }
        }
    }


    /**
     * Returns whether there are more elements in this <code>Enumeration</code>.
     */

    public boolean hasMoreElements() {
        findNext();

        return next != null;
    }


    /**
     * Returns the next element in the delegate enumeration which passes the
     * <code>accept</code> method.
     */

    public Object nextElement() throws NoSuchElementException {
        findNext();

        if (next == null)
            throw new NoSuchElementException();

        Object result = next;
        next = null;
        return result;
    }


    /**
     * Returns whether the specified object passes the filter.
     */

    public abstract boolean accept(Object element);


}